<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>侦听器</title>
    <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>

</head>
<body>
    <div id="app">
        <p>{{message}}</p>
    </div>    

    <script>
        var app = new Vue({
            el:"#app",
           data:{
               message:"你好"
           },
        //    监听器中的也是一个键值对，键是监听的变量，
           watch:{
               message:function(newVal,oldVal){
                   console.log("新值:"+newVal);
                   console.log("旧值:"+oldVal);
               }
           },
          
        });
    </script>
</body>
</html>